The present invention relates to a microcoil constructed using an additive technique on a substrate surface.
A type of microcoil coil is described in xe2x80x9cFirst Integrated Inductive Proximity Sensor with On-chip CMOS Readout Circuit and Electrodeposited 1 mm Flat Coil,xe2x80x9d Ph. A. Passeraub et al., Proceedings of Eurosensors XII, 1998. Microcoils like these are suitable only for small currents and achieve only a low inductance. They are therefore suitable for sensor purposes but not for switching applications requiring high currents and inductances, for example. If microcoils of the known design were to be used for high currents and inductances, this would have resulted in an extremely high requirement of substrate surface, because the inductance of the known coil can be increased only by adding additional coils on the outer circumference, so that for this reason alone, the surface requirement would increase in proportion to the inductance. At the same time, the cross section of the printed conductors would have to be increased for a greater current carrying capacity, but that would also lead to a greater surface requirement.
Although essentially the surface requirement can be reduced by forming a microcoil with several superimposed planes of conductors, as described in German Published Patent Application No. 196 40 676, such a coil design leads to the problem that the heat released by the current flowing through the conductor can no longer be dissipated as effectively as with a single-layer design. Therefore, with the same conductor cross section, the current carrying capacity of such a coil is lower than that of a coil whose conductors are arranged in a single plane.
The present invention creates a structure for a microcoil constructed using the additive technique, making it possible to construct coils having a high inductance and a low resistance suitable for high-current applications.
This advantage is achieved by the fact that the conductors of the coil are in contact with an electrically insulating body having at least some diamond or diamond-like carbon. Diamond has an extremely high thermal conductivity of approx. 20 W/cmK and a high breakdown field strength of approx. 107 V/cm, and it is thus equally suitable as an electric insulation material and a thermal conduction material. Diamond-like carbon (DLC) has in common with true diamond the sp3 or sp2 hybridization of the carbon atoms of its crystal structure, and therefore it has similarly advantageous thermal conduction and insulation properties.
The coil is advantageously surrounded by a sheathing of a magnetically shielding material to prevent the relatively strong magnetic fields that can be generated with such a microcoil from having feedback effects on adjacent circuits and also to improve the inductance of the coil as such. Such a material may be a nickel-iron alloy or a nickel-cobalt alloy, for example.
According to a first variant of the present invention, the insulating body is composed at least in part of a mixture containing diamond crystals and optionally containing oxide-nitride or polymer materials, for example, as additional components.
The coil according to the present invention can be manufactured especially easily if the mixture is a photolithographically structurable polymer material. This material can be applied to a large area of substrate surface, and the conductors of the coil can be made to grow, e.g., by galvanic techniques trenches produced in the material in the course of structuring.
According to a second preferred variant of the present invention, the insulating body includes at least one layer of diamond or diamond-like carbon extending over the entire cross section of the coil. There may be individual openings in the layer which do not significantly impair its thermal conductivity, in particular as passages for printed conductors.
For effective cooling of the conductors, the at least one layer of diamond or diamond-like carbon is preferably arranged in direct contact with the conductors to be cooled.
This second variant is especially advantageous in the case of a compact design of the coil, where the conductors are arranged in multiple planes. In this case, each plane is provided with at least one layer of diamond or diamond-like carbon.
Furthermore, the substrate carrying the coil is preferably a semiconductor substrate, and the coil is connected to an integrated circuit arranged in the substrate beneath it.
Additional advantages and features of the present invention are derived from the following description of embodiments with reference to the figures.